Fractures of the proximal femur are devastating events for individuals, particularly for the elderly for whom these types of injuries are relatively frequent. In the United States alone there are more than 300,000 hip fractures (Hudson et al., Clin. Orthop., pp. 59-66, 1998), and by the year 2050 the number is expected to double (Koval and Zuckerman, J. Am. Acad. Orthop. Surg., 2(3): 141-149, 1994; Montgomery and Lawson, Clin. Orthop., pp. 62-68, 1978).
Osteonecrosis of the hip, also known as avascular necrosis (AVN), aseptic necrosis, ischemic bone necrosis, or osteochondritis dissecans, is a condition where the blood supply to the femoral head is compromised, resulting in degeneration and collapse of the hip. AVN most commonly occurs in individuals between the ages of 30 and 60. Although it can occur in any bone, AVN most commonly affects the ends of long bones or the epiphysis, such as the femur. Other common sites are the humerus, knees, shoulders, and ankles. The disease can affect one or more bones at the same time or at different times. AVN can also be involved in other bone diseases, such as osteoarthritis.
A system and method of treating osteonecrosis is described in U.S. Pat. No. 6,827,720 (the '720 Patent). The '720 Patent describes a technique of drilling channels in bone (which is termed core decompression) and inserting growth factors followed by a plug (not containing growth factors), which compresses the growth factors. The channel is sealed with a plug or screw that is advanced into each channel and compacts the bone-growth-inducing compound. The bone-growth compound is therefore biased toward the distal end of the channel. The compacting event forces the compound into the necrotic section of bone, and the pressure causes the distal bone voids to be filled with bone-growth material. The plug or screw reinforces the subchondral bone and adds structural strength to the necrotic bone, preventing collapse of the bone.
Core decompression treatment involving drilling a hole into the femoral head and packing autograft or allograft bone is intended to stimulate the growth of blood vessels and new bone in the femoral head. Bone morphogenic protein (BMP) is known to stimulate both new bone and new blood vessel formation. Additionally, it is believed that the drilling procedure itself also stimulates bone formation by releasing indigenous growth factors within the surrounding bone. Overstuffing or overpacking of BMP on a collagen carrier, however, is associated with bone resorption prior to new bone formation because the overstuffing or overpacking results in too high of a concentration of BMP (see Burkus, et al., “Short-term effects of rhBMP-2/absorbable collagen sponge in a cancellous bone environment,” The Spine Journal 6:73S-74S (2006)). Bone resorption could result in further collapse of the hip if an excessively high concentration of BMP were used in core decompression. Such excessively high concentrations can arise when a carrier having the correct concentration is overpacked in the hole. A method to deliver BMP and other growth factors on a carrier for a core decompression procedure without overpacking would therefore maximize the potential for success.